This invention relates to the preparation of improved polymeric compounds containing one or more urea, urethane or thiourethane groups. More particularly, the invention relates to a method of improving the thermal stability and processability of the above polymeric compounds prepared by tin-containing catalysts.
U.S. Pat. No. 3,652,507 issued to Burk, Jr. et al on Mar. 28, 1973 describes an improved process for preparing urethane-type polymers by the condensation of cyclic nitrile compounds with nucleophilic compounds in the presence of a catalytic system comprised of a first metal selected from the metals of Groups III through V of the Periodic Chart, e.g., tin, and a second metal selected from the metals of Groups I and II and the iron series of Group VIII of the Periodic Chart, for example, an alkali metal. It has been discovered that when certain tin compounds are used in the process disclosed in this patent the polymeric product obtained has a very high molecular weight, making it particularly suitable for use in the manufacture of molded or extruded products. However, when these polymers are subjected to physical processing at elevated temperatures, such as is encountered in milling and molding operations, they have been found to undergo molecular weight reduction which results in a loss of physical properties, thus making the product unsuitable for many uses.
A method has now been discovered for treating urethane-type polymers prepared from catalyst systems containing these tin compounds which overcomes the above difficulty. Thus, urethane-type polymers of very high molecular weight which do not undergo molecular weight reduction upon physical processing at elevated temperatures can be prepared from cyclic nitrile compounds and nucleophilic compounds using catalyst systems containing tin compounds.
Accordingly, it is an object of the invention to present a method of preparing improved urethane-type polymers. It is another object of the invention to present a method of preparing high molecular weight urethane-type polymers which have a reduced tendency to undergo molecular weight degradation during physical processing at elevated temperatures. It is another object of the invention to present a method of improving the thermal stability of urethane-type polymers prepared from cyclic nitrile compounds and nucleophilic compounds by means of a tincontaining catalyst. These and other objects of the invention will become more readily apparent from the following description and examples.